单项选择题

Hydrocarbons, ______ by engine exhausts, react with nitrogen oxides in the presence of sunlight to form complex toxic gases.

A. are given off

B. give off
C. they are given off

D. given off
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单项选择题
Too much ______ can possibly lead to unhappiness, even to thoughts of suicide as few people have the courage to analyze themselves objectively and minutely.
A. retrospect

B. introspection
C. perspicacity

D. perspicuity
单项选择题
We listened dumb-struck, full of ______ to the shocking details of the corruption of the ex-president of the company.
A. incredulity
B. ingenuity
C. ingenuousness
D. incredibility
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